1. Field of the Invention
The present invention relates to a delay time measuring method and system of an echo request/response between stations in a network and a station and a program used in the same system, and more particularly to the delay time measuring method and system using an OAM (Operations, Administration and Maintenance) echo request/response frame in an RPR (Resilient Packet Ring) system, and the station and the program used in the same system.
2. Description of the Related Art
As a related packet communication technology in a ring network in which a plurality of node devices is connected through a bilateral dual ring line, the RPR (Resilient Packet Ring) system standardized in IEEE 802.17 is known (for example, Patent Reference 1 [Japanese Patent Application Laid-open No. 2004-242194]).
In the RPR system, each of stations being a node connected on a bilateral dual ring line has functions, by using a control packet being transmitted periodically by each station, and by advertising a physical address thereof on the bilateral dual ring line and collecting the adverised information to recognize a topology map (arrangement information) indicating an alignment order of each station. Also, each station has further functions of selecting a ring system near to a physical address of a destination by referring to the topology map when a packet is transmitted to the ring.
The IEEE 802.17 designates both an OAM echo testing function in the RPR system and also an OAM echo request/response frame to be used for OAM echo testing. According to OAM echo request/response frame specifications, a testing station transmits an OAM echo request/response frame to a station to be tested and confirms continuity between the stations by receiving the OAM echo response frame returned from the station to be tested.
The operation of the continuity confirming test using the OAM echo function in the RPR system is described by referring to FIGS. 5 to 8.
FIG. 5 shows an example of a basic configuration of the RPR system as a related art in which RPR stations 11 to 18 are arranged in the order of alignment of each station shown in FIG. 5 in the bilateral dual ring network connected by an outer ring and an inner ring. A specified MAC (Media Access Control) address is assigned to each of the RPR stations 11 to 18.
FIG. 6 shows an image of arrival of the OAM echo request frame transmitted to the RPR stations 11 to 14 in order to confirm continuity. FIG. 7 shows an image of arrival of the OAM echo response frame from the RPR station 14 through the RPR stations 13, 12, and 11. FIG. 8 shows a configuration of an OAM echo request/response frame designated by the IEEE 802.17 recommendation. In FIG. 8, the RPR frame is represented by a 128-bit width and a Padding region is a convenient region to represent the RPR frame by the 128-bit width (therefore, if the RPR frame is represented by an 8-bit width, the Padding region becomes unnecessary.).
When the continuity from the RPR station 11 to the RPR station 14 is confirmed, in the RPR station 11, an address value (its own address value) of the RPR station 11 is stored in the MAC (Media Access Control) source address of the OAM echo request/response shown in FIG. 8 and an address value of the RPR station 14 is stored in the MAC destination address and, as shown in FIG. 6, the continuity confirmation test between the RPR station 11 and RPR station 14 in the case when the OAM request is transmitted through the outer-side link is performed.
The intermediate RPR stations 12 and 13, since the received OAM echo request frame is not destined to their own addresses, perform an operation of bridge outputting of the received OAM request/response frame to a neighboring RPR station.
The RPR station 14, when receiving the OAM echo request frame destined to the address thereof, stores its own address in the MAC source address and returns, through an inner-side link, an OAM echo response frame in which the MAC address of the RPR station 11 being a destination is stored in the MAC destination address. The RPR station 11 completes the continuity confirmation by the OAM response frame received through the intermediate stations 13 and 12.
In the specification of the OAM echo request/response frame to be used for the OAM echo testing designated by the IEEE 802.17, only the function of confirming continuity between stations by a testing station's transmitting an OAM echo request frame and receiving an OAM response frame returned from the station to be tested, however, the function of measuring delay time between the stations is not included in the continuity testing using the OAM echo request/response frame.
The IEEE 802.17 designates a function of measuring an LRTT (Loop Round Trip Time) as a function of measuring delay time between stations. FIG. 9 shows a format of the LRTT request/response frame (in the case of 128-bit parallel transport).
In the LRTT measuring test designated by the IEEE 802.17, delay time between an RPR station carrying out the measurement and an RPR station to be measured is periodically measured. In this test, following operations are performed:    1. A measuring station, when sending out an LRTT request frame destined to a station to be measured, adds the sending-out time in the form of “LatencyTimeStamp” to the LRTT request frame.    2. A station to be measured, when receiving the LRTT request frame, sends back the LRTT response frame to the measuring station. At this point of time, the station to be measured adds receiving time of the LRTT request frame in the form of “tailLatencyIn” and sending-out time of the LRTT response frame in the form of “tailLatencyOut” to the LRTT response frame.    3. The measuring station having received the LRTT response frame calculates the delay time between the measuring station and the station to be measured by computing the receiving time using an expression [t4−t1−(t3−t2)],
where t1 denotes the “LatencyTimeStamp”; t2 denotes the “tailLatencyIn”; t3 denotes the “tailLatencyOut”; and t4 denotes the “receiving time”.
The aim of applying the subtraction (t3−t2) in the above expression is to calculate net delay time required for passing through a ring by excluding time taken for returning the frame by the station to be measured.
However, the LRTT measuring method has problems. That is, the IEEE 802.17 recommendation designates that the LRTT testing is to be performed by setting a service class to be A0 class (fixed) and, therefore, the value obtained by using the LRTT is a value measured with the first priority service class being set. As a result, a problem arises that it is impossible to measure the time by setting an arbitrary service class. Another problem is that; since the LRTT testing is an inner process of measuring the time periodically, a user or an operator cannot use the testing as a means to confirm actual delay time.
On the other hand, in the IEEE 802.17 Maintenance, a proposal is made as an extended plan in which the information about the LatencyTimeStamp, TailLatencyIn, and TailLatencyOut is provided in the payload of the OAM echo request/response frame to add a function of measuring delay time being equivalent to the LRTT function to the OAM echo testing function.
In the IEEE 802.17 Maintenance, there is a description of the addition of the information about the LatencyTimeStamp, the TailLatencyIn, and the TailLatencyOut, however, there is no description of how the information described above is provided. Presuming that the above information is provided in the frame being the same as the LRTT request/response frame, the OAM echo request/response frame as shown in FIG. 10 is prepared in which the LatencyTimeStamp, TailLatencyIn, and TailLatencyOut are provided in the order shown in FIG. 10 after the response control in the frame.
By using the extended OAM echo request/response frame format shown in FIG. 10, confirmation of continuity between stations and measurement of delay time can be simultaneously performed. Moreover, in the case of the OAM echo testing, there is no designation in the IEEE 802.17 recommendation as to which service class is used for the testing and, therefore, testing is allowed by using any service class. As a result, by using the extended OAM echo request/response frame format, delay time can be measured by setting any service class.
However, the extended OAM echo request/response frame format, as shown in FIG. 10, is so configured that the LatencyTimeStamp, the TailLatencyIn, and the TailLatencyOut are provided as a time stamp written after the response control in the frame and delay time measured between a measuring station and a station to be measured using the OAM echo request/response frame is calculated, as in the case of the LRTT measurement, by using the calculating the expression [t4−t1−(t3−t2)], where t1 denotes the “LatencyTimeStamp”; t2 denotes the “tailLatencyIn”; t3 denotes the “tailLatencyOut”; and t4 denotes the “receiving time”.
Accordingly, when this configuration is employed, time information received by the receiving section of the measuring station is used as the receiving time of a response frame and, therefore, time-synchronization between the receiving section and transmitting section within not only the measuring station but also the station to be measured is required and, further, the receiving of the response frame and calculation of the delay time have to be simultaneously performed.